Clean Coastal Waters Understanding and Reducing the Effects of Nutrient Pollution (2000) / Chapter Skim
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9 Source Reduction and Control
9 Source Reduction and Control
Pages 269-310
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From page 269... ...
· Options to minimize nutrient export from agricultural areas include manure management strategies, careful estimation of native nutrient availability and crop requirements, and supplemental fertilizer application timed to meet crop demand. Watershed-scale implementation of best management practices needs to be targeted to ensure maximum reduction in nitrogen and phosphorus export.
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From page 270... ...
This chapter explores management strategies designed to reduce nutrient inputs. Because agricultural runoff is one of the greatest challenges in nutrient control, considerable attention is focused on control of agricultural sources, followed by control of atmospheric sources, urban sources, and control by other mechanisms.
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From page 271... ...
i, O In In o . _ z 20 ,' ~ Conventional _/ \ to no-till · -- _ ~ Nitrogen \ >~ Gullies treated ~1980 1985 1990 1994 FIGURE 9-1 Annual nitrogen and phosphorus loss into the Little Washita River from a wheat-dominant and grass-dominant sub-watershed.
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From page 272... ...
. Source Management Animal Feeding of Nitrogen and Phosphorus Both nitrogen and phosphorus are important dietary nutrients for animals and have a key role in various metabolic functions (NRC 1989~.
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From page 273... ...
Reducing Off-Farm Inputs of Nitrogen and Phosphorus The accumulation of nutrients on many animal feeding operations where on-farm crop production is supplemented by feed inputs is generally not as great as in other operations where the animals depend primarily on off-farm feed. The distinguishing feature among these animal operations is the breakdown between the amount of crops produced on a
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From page 274... ...
Reduction of nitrate loading to surface waters in the Mississippi River basin can be achieved by reducing nitrate sources and controlling drainage (NOAA l999b)
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From page 275... ...
Steps in applying this principle include: · estimating the nitrogen requirement of the next crop (expected yield) ; · evaluating nitrogen available from native sources (soil nitrogen mineralization, residual soil nitrate, irrigation water, etc.~; · subtracting the available native nitrogen from the crop nitrogen requirement to estimate supplemental nitrogen needs; · determining the most appropriate source of supplemental nitrogen (manure, fertilizer, crop residues)
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From page 276... ...
For fertilizer nitrogen, this is a relatively easy task because it can be applied just before the period of rapid crop nitrogen uptake. Applying nitrogen when needed does not itself ensure adequate control of losses.
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From page 277... ...
Today's concerns with phosphorus are caused by the realization that soils that are considered "optimum" in soil test phosphorus (or perhaps only slightly over fertilized) from a crop production perspective may still provide environmentally significant quantities of phosphorus in surface runoff and erosion.
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From page 278... ...
For example, subsurface injection or incorporation in rocky soils may be difficult, and without manure storage, farmers who contract out the cleaning of poultry houses will have little flexibility for when manure or litter is applied. Manure Management As discussed in Chapter 5, animal wastes are a major part of the nutrient over-enrichment problem, and management efforts are complicated by the long distances that feedstocks are transported.
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From page 279... ...
An increased nitrogen:phosphorus ratio of manure would more closely match crop nitrogen and phosphorus requirements. One approach to better manure management would be to establish a mechanism to facilitate movement of manures from surplus to deficit areas.
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From page 280... ...
Such transport management measures include terracing, contour tillage, cover crops, buffer strips, riparian zones, and impoundments. These transport measures are generally more efficient at reducing particulate phosphorus rather than dissolved phosphorus.
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From page 281... ...
Data from farms within the United Kingdom Nitrate Sensitive Areas Scheme show that such crops are compatible with commercial farming systems, relatively inexpensive to manage, and can reduce nitrate losses by about 50 percent (Sharpley and Lord 1998~. For phosphorus, crop cover at any time during the period when agricultural runoff can occur will help protect against total phosphorus loss but will be less effective against losses of dissolved phosphorus (Sharpley and Smith 1991~.
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From page 282... ...
Because of differing chemistry and flow pathways of nitrogen and phosphorus in soil and through the watershed, these narrowly targeted strategies often are in conflict and lead to compromised water quality remediation. For example, basing manure application on crop nitrogen requirements to minimize nitrate leaching to groundwater increases soil phosphorus and enhances potential phosphorus surface runoff losses.
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From page 283... ...
However, it is evident that several factors are critical to effective BMP implementation. These factors include targeting watersheds that will respond most effectively to BMPs, identifying critical source areas of nutrient export, as well as accounting for both watershed and estuary response time and equilibration (capacity to buffer added nitrogen and phosphorus)
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From page 284... ...
BMPs included barnyard runoff control, milkhouse waste treatment, and construction and use of manure storage facilities. Phosphorus losses were lower than before BMPs.
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From page 285... ...
For the example of the two Vermont watersheds in Table 9-3, the most effective BMP installation priority would be barnyard runoff control, followed by milkhouse waste treatment, and then animal waste storage facilities. Without careful targeting of critical nutrient source controls within a watershed, BMPs may not produce the expected reductions in nitrogen and phosphorus export.
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From page 286... ...
These BMPs included control of barnyard runoff, milkhouse waste treatment, and construction of waste storage facilities. However, there was no apparent reduction in either dissolved or total phosphorus concentration in runoff with increasing percent of animals in a watershed under a BMP (dashed lines; Figure 9-2~.
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From page 287... ...
m ·3 0.2 In In o 0.4 0.3 0.1 o Cal O -0.1 Mud Hollow Brook Watershed, Vermont With extreme events Without extreme events Total Phosphorus Dissolved Phosphorus FIGURE 9-3 Effect of BMP implementation on total and dissolved phosphorus loss from Mud Hollow Brook watershed, Vermont, 1985 to 1989, with and without inclusion of extreme flow events. Positive values indicate an increase in phosphorus loss and negative values and decrease in phosphorus loss with BMP implementation (modified from Meals 1990~.
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From page 288... ...
Also, stakeholder alliances have been developed among state, federal, and local groups, producers, and the public to identify problems, focus resources, and implement BMPs in Chesapeake Bay and the New York City watershed, for example. ATMOSPHERIC SOURCES As discussed in Chapter 5, atmospheric deposition is a significant source of nitrogen loadings to some estuaries and other coastal waters, particularly in the northeastern United States.
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From page 289... ...
In the United States, most of the ammonium deposition comes from agricultural sources, particularly from animal wastes but also from volatilization of fertilizers, while the oxidized nitrogen comes principally from the combustion of fossil fuels. For nitrogen deposition directly onto the water surface of an estuary, reductions in the sources of nitrogen to the atmosphere are the only possible approach to control.
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From page 290... ...
finds that, as cars age and the emission control equipment breaks down, better fuel economy is strongly associated with low emissions, at least for CO and HC. If vehicle emissions in fact vary considerably by year, make and size (Kahn 1996)
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From page 291... ...
1997~. To date, policies designed to reduce NOx emissions have stemmed not from concerns about excess nutrient loadings to waterbodies, but rather from the other environmental impacts of NOx emissions.
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From page 292... ...
Because of concerns about the health effects of ozone, considerable attention has been focused on efforts to reduce NOx emissions. While not designed specifically to reduce nutrient loadings to waterbodies, these efforts can be expected to have eutrophication-related benefits as well.
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From page 293... ...
In addition, motor vehicle emissions standards (i.e., limits on allowable grams of emissions per mile) are set by the Clean Air Act.
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From page 294... ...
Communities that have bans on phosphate detergents typically enjoy a reduction of approximately 32 and 39 percent on total phosphorus and orthophosphate concentrations, respectively, in domestic wastewater (WEF 1998~. Biologically-based secondary treatment typically reduces total nitrogen by approximately 31 percent and total phosphorus by approximately 38 percent (NRC 1993a)
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From page 295... ...
. Depending on the process employed, up to 97 percent of total nitrogen and 99 percent of total phosphorus may be removed from the waste stream (Table 9-5~.
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From page 297... ...
Discharge from septic tank systems is commonly estimated as 280 liters per capita per day (1 cape day- with typical effluent concentrations of 40 to 80 mg 1-~ for total nitrogen and 11-31 mg 1-~ for total phosphorus (Novotny et al.
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From page 298... ...
Other factors that affect the degree of nitrogen removal include temperature and the density of the soil in the septic tank fields. Urban Diffuse Source Discharges Urban diffuse nutrient sources include both runoff from streets and storm sewers and combined sewer overflows.
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From page 299... ...
might remove 30 to 40 percent of total nitrogen and 50 to 60 percent of total phosphorus, with removal increasing as the dissolved forms of nitrogen and phosphorus
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From page 300... ...
Their capacity for nutrient removal can be considerable (Mitsch and Gosselink 1986~. Hence, protection of coastal wetlands and tidal exchange is an important water quality consideration for coastal waters.
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From page 301... ...
Schueler (1992) indicates projected removal rates for total phosphorus and total nitrogen on the order of 40 to 60 percent and 20 to 30 percent, respectively.
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From page 302... ...
When finished, this study will provide a definitive statement about the effectiveness of urban BMPs. OTHER MITIGATION OPTIONS Regional Stormwater Control Facilities Location as well as type of BMPs play an important role in control of nonpoint source runoff.
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From page 303... ...
In this way, combined sewer overflow loadings to San Francisco Bay are avoided, except for very high storm events. Hydrologic/Hydraulic Alterations in the Watershed The history of human development is one of encroachment upon wetlands and waterways, and loss of wetlands in coastal areas is substantial.
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From page 304... ...
The same principles apply to estuaries and coastal waters (Ingrid et al.
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From page 305... ...
While fishery practices in coastal areas may have impacts on nutrient enrichment in coastal areas, it would be exceedingly difficult to manage this through manipulations of fishery populations. Benthic filter feeders such as oysters, mussels, and many species of clams can have a major influence on phytoplankton populations in coastal waters (Lucas et al.
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From page 306... ...
It follows that a reduction in pollution can sometimes lead to a decrease in HAB frequency or magnitude. It should be emphasized, however, that it is exceedingly difficult to predict with any certainty what the effect of pollution control strategies will be on HAB incidence, except in situations where the pollution loading is massive (e.g., in Tolo Harbour or the Inland Sea of lapan [Box 4-2~)
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From page 307... ...
The potential benefits of reductions of nutrient loadings in terms of decreased frequency and severity of HABs should be one of several considerations driving pollution policy decisions in estuarine and coastal management programs, but it should not be the sole justification. Marketable Permits Prior to 1990, marketable permits played only a minor role in environmental policy design, but the 1990 Clean Air Act Amendments promoted the use of marketable permits for sulfur dioxide emissions and provided an impetus for increased attention to this policy instrument.
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From page 308... ...
In most cases we know how to minimize nutrient export and input to coastal waters (the science is there) , so that the major barriers to implementation now involve overcoming economic constraints, societal pressures, and political forces.
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From page 309... ...
Economic data is also needed to help determine the economic benefits of management strategies and to see implementation costs in relation to the relative costs of different problems caused by nutrient over-enrichment. The Clean Air Act may be as important as the Clean Water Act in protecting the nation's coastal waters from nitrogen pollution.
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From page 310... ...
However, managers have options beyond source control. For coastal waters with smaller tributary areas, mitigation strategies such as enhancement of coastal wetlands might be a possibility.
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